Transcript Section 2 The Sun

Chapter 20
Formation of the Solar System
Table of Contents
Section 2 The Sun: Our Very Own Star
Section 4 Planetary Motion
Chapter 20
Section 2 The Sun: Our Very Own Star
Bellringer
Henry David Thoreau once said, “The sun is
but a morning star.”
What do you think this quotation means?
Chapter 20
Section 2 The Sun: Our Very Own Star
Objectives
• Describe the basic structure and composition
of the sun.
• Explain how the sun generates energy.
• Describe the surface activity of the sun, and
identify how this activity affects Earth.
Chapter 20
Section 2 The Sun: Our Very Own Star
The Structure of the Sun
• The sun is basically a large ball of gas made mostly
of hydrogen and helium held together by gravity.
• Although the sun may appear to have a solid
surface, it does not. The visible surface of the sun
starts at the point where the gas becomes so thick
that you cannot see through it.
• The sun is made of several layers, as shown on the
next slide.
Chapter 20
Section 2 The Sun: Our Very Own Star
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun
• The sun has been shining on the Earth for about
4.6 billion years. Many scientists once thought
that the sun burned fuel to generate its energy.
• The amount of energy that is released by
burning would not be enough to power the sun. If
the sun were simply burning, it would last for only
10,000 years.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• Burning of Shrinking? Scientists later began
thinking that gravity was causing the sun to slowly
shrink and that gravity would release enough energy
to heat the sun.
• While the release of gravitational energy is more
powerful than burning, it is not enough to power the
sun. If all of the sun’s gravitational energy were
released, the sun would last only 45 million years.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• Nuclear Fusion Albert Einstein showed that matter
and energy are interchangeable. Matter can change
into energy according to his famous formula:
E  mc2
(E is energy, m is mass, and c is the speed of light.)
• Because c is such a large number, tiny amounts of
matter can produce a huge amount of energy.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• The process by which two or more low-mass nuclei
join together, or fuse, to form another nucleus is called
nuclear fusion.
• In this way, four hydrogen nuclei can fuse to form a
single nucleus of helium. During the process, energy
is produced.
• Scientists now know that the sun gets its energy
from nuclear fusion.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• Fusion in the Sun During fusion, under normal
conditions, the nuclei of hydrogen atoms never get
close enough to combine.
• The reason is that the nuclei are positively charged,
and like charges repel each other, just as similar poles
on a pair of magnets do.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• In the center of the sun, however, temperature and
pressure are very high.
• As a result, hydrogen nuclei have enough energy to
overcome the repulsive force, and hydrogen fuses
into helium, as shown on the next slide.
Chapter 20
Section 2 The Sun: Our Very Own Star
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• Energy produced in the center, or core, of the sun
takes millions of years to reach the sun’s surface.
• Energy passes from the core through a very dense
region called the radiative zone. The matter in the
radiative zone is so crowded that light and energy
are blocked and sent in different directions.
Chapter 20
Section 2 The Sun: Our Very Own Star
Energy Production in the Sun, continued
• Eventually, energy reaches the convective zone.
Gases circulate in the convective zone, which is
about 200,000 km thick.
• Hot gases in the convective zone carry the energy
up to the photosphere, the visible surface of the sun.
• From the photosphere, energy leaves the sun as
light, which takes only 8.3 minutes to reach Earth.
Chapter 20
Section 2 The Sun: Our Very Own Star
Solar Activity
• The churning of hot gases in the sun, combined
with the sun’s rotation, creates magnetic fields that
reach far out into space.
• The constant flow of magnetic fields from the sun
is called the solar wind.
• Sometimes, solar wind interferes with the Earth’s
magnetic field. This type of solar storm can disrupt
TV signals and damage satellites.
Chapter 20
Section 2 The Sun: Our Very Own Star
Solar Activity, continued
• Sunspots The sun’s magnetic fields tend to slow
down activity in the convective zone. When activity
slows down, areas of the photosphere become cooler
than the surrounding area.
• These cooler areas show up as sunspots. Sunspots
are cooler, dark spots of the photosphere of the sun.
Some sunspots can be as large as 50,000 miles in
diameter.
Chapter 20
Section 2 The Sun: Our Very Own Star
Sunspots
Click below to watch the Visual Concept.
Visual Concept
You may stop the video at any time by pressing
the Esc key.
Chapter 20
Section 2 The Sun: Our Very Own Star
Solar Activity, continued
• Climate Confusion Sunspot activity can affect the
Earth. Some scientists have linked the period of low
sunspot activity, 1645-1715, with a period of very low
temperatures that Europe experienced during that
time, known as he “Little Ice Age.”
Chapter 20
Section 2 The Sun: Our Very Own Star
Solar Activity, continued
• Solar Flares The magnetic fields responsible for
sunspots also cause solar flares. Solar flares are
regions of extremely high temperatures and brightness that develop on the sun’s surface.
• When a solar flare erupts, it sends huge streams of
electrically charged particles into the solar system.
Solar flares can interrupt radio communications on
the Earth and in orbit.
Chapter 20
Section 4 Planetary Motion
Bellringer
A mnemonic device is a phrase, rhyme, or
anything that helps you remember a fact. Create
a mnemonic device that will help you differentiate
between planetary rotation and revolution.
Record your mnemonic device in your science
journal.
Chapter 20
Section 4 Planetary Motion
Objectives
• Explain the difference between rotation and
revolution.
•Describe three laws of planetary motion.
• Describe how distance and mass affect
gravitational attraction.
Chapter 20
Section 4 Planetary Motion
A Revolution in Astronomy
• Each planet spins on its axis. The spinning of a
body, such a planet, on its axis is called rotation.
• The orbit is the path that a body follows as it
travels around another body in space.
• A revolution is one complete trip along an orbit.
Chapter 20
Section 4 Planetary Motion
Earth’s Rotation and Revolution
End of Chapter 20